1. Field of the Invention
The present invention relates generally to methods of bonding and sealing together metal parts. In particular, the present invention relates to processes of fabricating and repairing hollow beryllium structures, such as thermal control devices and other pressure vessels for space flight applications, through high temperature isostatic pressure bonding.
2. Background of the Invention
Typically beryllium vessels have been formed by welding or brazing using a filler metal, such as aluminum or silver. The problem with such vessels is that the coefficient of thermal expansion (CTE) of the filler metal is substantially different from that of the bulk beryllium. The use of a filler metal for joining results in low strength properties. Although these methods are adequate for systems that require lower strength properties and do not go through a large range of temperatures during thermal cycling, they reduce the reliability of the system.
U.S. Pat. No. 3,964,667 to Anderson teaches diffusion bonding of beryllium parts under pressure, using a coating of nickel between the beryllium parts. U.S. Pat. No. 5,615,826 to Dixon et al. teaches joining of beryllium parts by welding with an aluminum alloy (e.g., aluminum and silicon).
These bonding methods should not be used with pressure vessels having high internal pressures and that are subjected to large temperature variations, AT. One example of such a vessel is a space flight Thermal Storage Unit (TSU). TSUs translate across a large temperature swing (.DELTA.T.about.300.degree. K), and require large factors of safety in the bond area to meet the aerospace requirements.
A need therefore exists for improved bonding methods that provide the necessary reliability.